In the transmission of currents at high voltage and particularly in distribution systems which are underground, numerous splices or connections are necessary. These are conveniently effected using metallic sleeves crimped to bare ends of the cables followed by applying suitable insulation and shielding. Other methods have been used as described in some detail in U.S. Pat No. 4,079,189. As recognized in that patent, a major problem in such splices is the occurrence of corona discharge in air pockets around the splice. Such discharge tends to deteriorate cable insulation and create interference at many wavelengths of radio emission, i.e. static. Suppression of the discharge is therefore most important.
In U.S. Pat. No. 4,079,189 an insulator is provided with inner and outer semiconductive sections and end caps and an intermediate insulative section. The inner semiconductive section has a plurality of circumferentially spaced ribs extending inwardly. The ribs extend over a major portion of a crimped metallic connector of cable ends and contact the connector under compression as a result of deformation and bending. It would appear that insulators as described might be difficult to fabricate using a molded inner semiconductive ribbed section. It would further appear that the force with which the ribs contact the connector might be relatively weak. It is an object of the present invention to provide an insulator for splices of high voltage cables which is readily manufactured and provides good insulation and suppression of corona discharge.
In accordance with the above and other objects of the invention it has been found that a convenient and efficient process for the production of insulating corona discharge suppressing shields for splices of high voltage lines comprises the steps of applying a tube of semiconductive elastomeric material having a wall of substantially uniform thickness to a mandrel having a pattern of depressions in a raised portion thereof, placing on said mandrel, positioned apart from said tube, end caps of generally elongated tubular form having outer and inner ends and having outer termination segments distal to said tube of uniform internal and external diameter and inner enlarged segments having variable external diameter and internal diameter varying from being equal to the internal diameter of said terminal segment to being greater than the external diameter of said terminal segment, placing a form or mold having a sprue opening at least around and between the enlarged segments of said end caps and injecting elastomer composition curable to insulative material through said sprue hole around said semiconductive tube and in said end caps while forcing said tube into the depressions in said mandrel. In a preferred embodiment of the invention the outer end of the termination segment of each end cap is formed with at least double undercutting toward the internal diameter as further described below. After addition of an outer annular semiconductive cover extending onto and between the enlarged segments of said end caps, there is obtained an insulative corona discharge suppressing shield for positioning over and along a splice in high voltage cable of generally circular cross section having semiconductive covering and insulating covering and an inner conductor and having an electrical connector electrically joining two bare ends of said conductor, said shield comprising two end caps having openings therein adapted to engage said semiconductive covering electrically, annular inner and outer semiconductive sections and an insulative section having inwardly directed bosses over at least a portion thereof extending inward and being integrally bonded at least to said inner semiconductive section and said end caps, said inner semiconductive section having a wall of substantially uniform thickness and further being urged inwardly by said bosses into electrical contact with said electrical connector when said shield is positioned on a high voltage cable splice.
It is found advantageous to have an inner semiconductive section of substantially uniform wall thickness to facilitate sliding of and positioning the sleeve over cables because the lesser stiffness over molded protuberances of semiconductive material permits easier deformation during installation. The urging inwardly of the inner semiconductive section by bosses provides superior electrical contact and enhances the reliability of the installed sleeve.